In the battle of the bulge, does a slice of bread in the morning affect you differently than one eaten at night?

While almost every diet plan on the market right now encourages you to eat most of your carbohydrates in the morning — the theory goes that eating your carbs early in the day gives you time to "burn them off" throughout the rest of the day — there has actually been relatively little evidence to support this popular notion. And now a new study has the potential to turn this piece of conventional wisdom on its head.

In the study, published in the October issue of the journal Obesity, 78 obese (Body Mass Index, or BMI, greater than 30) police officers were assigned to two similar weight loss diets for six months. In the first (or control) diet, the subjects were put on a calorie-reduced diet that provided between 1,300 and 1,500 calories per day, depending on individual need. The percentage of calories from protein (20 per cent; slightly higher than a typical Canadian diet), fat (30 to 35 per cent; about average for Canadians), and carbohydrates (45 to 50 per cent; slightly less than typical) were kept steady throughout the study, and carbohydrates were evenly distributed throughout the day.

In the experimental group, the calorie, protein, fat and carbohydrate intakes were kept the same as the control group, but the majority of the carbohydrates were reserved for the evening meal.

At the end of the six-month experimental period, both groups lost weight, but the carbs-in-the-evening group did better: They lost an average of 11.6 kg (25.5 lbs.) versus the control group’s 9.1 kg (20 lbs.). The experimental group also saw their waist circumference, a tool for estimating disease risk, shrink by 11.7 cm, versus 9.4 cm for the control group, and their body fat percentage drop by 7 per cent, versus 5.3 per cent for controls, though these differences were not pronounced enough to be considered statistically significant, meaning the result could have been because of chance.

Aside from physical changes, the carbs-at-night group also reported feeling less hungry after six months on the diet, and were less preoccupied with food than their counterparts. They also saw greater improvements in insulin levels (a hormone that helps to control blood sugar), and trends toward larger improvements in fasting blood sugar and cholesterol levels.

Some of these surprising findings could be explained by differences in two key hormones, leptin and adiponectin, observed between the two groups. Leptin is a hormone that helps us to feel full; when levels decline, either in the short-term between meals, or in the long-term during weight loss, we feel more hungry. While most weight loss studies have shown that leptin levels drop as we lose weight, the trend was not observed in the experimental group in this study. In other words, while weight loss usually breeds hunger, those who ate most of their carbs at dinner did feel the effect.

Similarly, while adiponectin, a hormone that helps to speed carbohydrate and fat metabolism, tends to be lower in obese individuals, those who reserved their carbs for dinner saw levels of the hormone rise throughout the study, more so than those who spread their carbs throughout the day.

So what does this all mean for the average person? Because the study was conducted on obese individuals who were generally healthy, it’s not possible to say whether we would see the same effect in a regular gym-goer who wants to shed body fat, or for an overweight person with type two diabetes or heart disease. But the results are intriguing, in large part because they clearly buck the popular trend to avoid carbs at night, and should lead to more research in the area.

It’s also worth noting that, while the experimental group did eat most of their carbohydrates at night, their total carbohydrate intake was still lower than most people would typically eat. While their daytime routine consisted of very few carbohydrates (largely from vegetables or vegetable soup as well as plain yogurt), their dinnertime meal included one to two cups of cooked pasta, corn or legumes, or two to four slices of bread, along with some fruit or fruit yogurt or a small dessert — quantities that are still far less than you would find in an average restaurant meal.

If you are thinking of experimenting with this diet regime (which, incidentally, was inspired by metabolic changes observed during the Muslim fasting period of Ramadan), realize that this is not an excuse to carb-load (or overload on anything) when you sit down to dinner tonight.